Tip Size Research Articles

Light-modulated van der Waals force microscopy

Atomic force microscope generally works by manipulating the absolute magnitude of the van der Waals force between tip and specimen. This force is, however, less sensitive to atom species than to tip-sample separations, making compositional identification difficult, even under multi-modal strategies or other atomic force microscopy variations. Here, we report the phenomenon of a light-modulated tip-sample van der Waals force whose magnitude is found to be material specific, which can be employed to discriminate heterogeneous compositions of materials. We thus establish a near-field microscopic method, named light-modulated van der Waals force microscopy. Experiments discriminating heterogeneous crystalline phases or compositions in typical materials demonstrate a high compositional resolving capability, represented by a 20 dB signal-to-noise ratio on a MoTe2 film under the excitation of a 633 nm laser of 1.2 mW, alongside a sub-10 nm lateral spatial resolution, smaller than the tip size of 20 nm. The simplicity of the light modulation mechanism, minute excitation light power, broadband excitation wavelength, and diversity of the applicable materials imply broad applications of this method on material characterization, particularly on two-dimensional materials that are promising candidates for next-generation chips.

Temperature dependence of gold nanostar particles morphology and its SERS application

ABSTRACT Gold nano-star particles (GNS) have broad application prospects in Raman enhancement, photovoltaic, and catalysis fields because of the hot spot effect of their tip structure. However, metal nanoparticles will accumulate heat during applications of high-power laser-focused irradiation, which may lead to the morphological degradation of the nanoparticles. In this paper, we have studied the effect of annealing temperature on the surface tip structure of GNS. Firstly, GNS with the multi-tip structure were synthesised by the two-step method, and GNS thin films were prepared by self-assembly technique without auxiliaries. By means of SEM characterisation, the film is found to be compact and uniform. Secondly, we systematically studied the morphology degradation of GNS at 100°C, 150°C, 200°C and 250°C. The results show that the tip of GNS does not change obviously until the temperature reaches 200°C. Then the four kinds of GNS films were used as surface-enhanced Raman scattering (SERS) substrates, and their Raman enhancement properties have been studied with adenine as the analyte, and stronger Raman enhancement effect can be found for the tip of nanoparticles. For a SERS substrate corresponding to an annealing temperature of 100°C, we have obtained the limit sensitivity of adenine molecule of 10−9 M. Finally, the surface electric field distribution and local resonance spectrum curves of four kinds of gold nanoparticles with different tip sizes were simulated theoretically by using the finite element method, and the results are consistent with the experimental data.

Modeling Conformational Transitions of Biomolecules from Atomic Force Microscopy Images using Normal Mode Analysis.

Observing a single biomolecule performing its function is fundamental in biophysics as it provides important information for elucidating the mechanism. High-speed atomic force microscopy (HS-AFM) is a unique and powerful technique that allows the observation of biomolecular motion in a near-native environment. However, the spatial resolution of HS-AFM is limited by the physical size of the cantilever tip, which restricts the ability to obtain atomic details of molecules. In this study, we propose a novel computational algorithm designed to derive atomistic models of conformational dynamics from AFM images. Our method uses normal-mode analysis to describe the expected motions of the molecule, allowing these motions to be represented with a limited number of coordinates. This approach mitigates the problem of overinterpretation inherent in the analysis of AFM images with limited resolution. We demonstrate the effectiveness of our algorithm, NMFF-AFM, using synthetic data sets for three proteins that undergo significant conformational changes. NMFF-AFM is a fast and user-friendly program that requires minimal setup and has the potential to be a valuable tool for biophysical studies using HS-AFM.

Combining Thermotherapy with Shoot Tip Culture or Cryotherapy for Improved Virus Eradication from In Vitro Actinidia macrosperma.

In recent years, kiwifruit viral diseases have become increasingly prevalent in kiwifruit-producing regions of China, significantly impacting both the yield and quality of kiwifruit. This has emerged as a significant constraint on the healthy and sustainable development of the kiwifruit industry. The use of virus-free propagation materials has been proven the most effective strategy for controlling plant viral diseases. In the present study, shoot tip culture, shoot tip cryotherapy, and their combinations with thermotherapy were established to eradicate Actinidia virus A (AcVA), Actinidia virus B (AcVB), and Actinidia chlorotic ringspot-associated virus (AcCRaV) from Actinidia macrosperma. Additionally, the impact of shoot tip size on virus eradication was evaluated. Among the three confirmed viruses, regardless of the procedure, AcVB was the easiest to eradicate, followed by AcVA and AcCRaV. Combining thermotherapy with shoot tip culture or cryotherapy resulted in a higher virus-free frequency (up to 27.3 and 50%, respectively) than shoot tip culture or cryotherapy alone (0 to 20%). Notably, the combination of thermotherapy and 0.5- to 1-mm shoot tip cryotherapy was shown to be the most effective protocol for virus eradication from A. macrosperma, which produced 50% of regenerated shoots free from all the tested viruses. To the best of our knowledge, this is the first report on virus elimination from kiwifruit infected with multiple viruses based on conventional shoot tip culture and shoot tip cryotherapy.

Clinical and genetic features of Fanconi anemia associated with a variant of FANCA gene: Case report and literature review.

Fanconi anemia (FA) is a hereditary disease caused by mutations in the genes involved in the DNA damage repair pathway. The FANCA gene is the most commonly pathogenic gene, accounting for more than 60% of all causative genes. The clinical case is a 3-year-old boy showed mild anemia and scattered bleeding spots the size of a needle tip all over his body. Compound heterozygous mutation was identified in the FANCA gene in the FA case: c.1A > T from the father in exon 1; the deletion of chr16: 89857810-89858476 (exon13-14 del) from the mother; finally, the patient was diagnosed as Fanconi anemia. After diagnosis, the child received chemotherapy (Ara-C + Flu + Cy + ATG). Then, the hematopoietic stem cell transplantation and unrelated umbilical cord blood transfusion were performed. The child is recovering well and is in regular follow-up. The discovery of new mutations in the FANCA gene enriches the genetic profile of FA and helps clinicians to further understand this disease and guide genetic counseling and prenatal diagnosis. Whole-exome sequencing is a powerful tool for diagnosing FA.

Effects of adhesive and frictional contacts on the nanoindentation of two-dimensional material drumheads

Nanoindentation of suspended circular thin films, dubbed drumhead nanoindentation, is a widely adopted technique for characterizing the mechanical properties of micro- or nano-membranes, including atomically thin two-dimensional (2D) materials. This method involves suspending an ultrathin specimen over a circular microhole and applying a precise indenting force at the center using an atomic force microscope (AFM) probe. Classical solutions assuming a point load and a fixed edge, which are referred to as Schwerin-type solutions, are commonly used to estimate Young’s modulus of the membrane material out of load–deflection measurements. However, given the widespread experimental evidence for adhesive and frictional contacts between the probe tip and the membrane, as well as sliding between the membrane and its supporting substrate, quantitative investigations of the effects of these interactions are required. In this paper, we formulate a boundary value problem to rigorously model such effects, ensuring relevance to experimental operations. Our numerical analyses reveal that the adhesive effect at the tip-membrane interface diminishes as the indentation depth increases or the tip size decreases. Furthermore, frictional interactions at this interface shift the maximum membrane stress from the center to the tip-membrane contact line with increasing indentation depth and interfacial shear stress. At large indentation depths, the size of the indenter tip and the sliding of the membrane-substrate are found to have a large effect on the indentation load–deflection relationship. Thus, we propose a new approximate formula for this relationship assuming a non-adhesive and frictionless spherical tip of a finite radius and a slippery contact with the supporting substrate. This formula is more accurate than the widely used Schwerin-type solution. It can be used to simultaneously extract the in-plane stiffness of the membrane and the shear strength at the membrane-substrate interface.

Genicular nerve radiofrequency ablation practice patterns: A survey study of the International Pain and Spine Interventional Society

IntroductionChronic knee pain often results from degenerative conditions such as knee osteoarthritis (OA) and can worsen after surgical interventions like total knee arthroplasty (TKA). Knee OA affects approximately 86 million individuals globally, leading to decreased function, mobility limitations, and disability. While TKA is a common surgical treatment for refractory knee OA, though up to 20 % of patients experience chronic post-operative knee pain worse than their pre-operative pain. Genicular nerve radiofrequency ablation (GnRFA) has emerged as a promising intervention for knee OA pain unresponsive to conservative management and for chronic post-TKA pain. GnRFA is an evidence-based technique supported by multiple prospective cohort studies and randomized controlled trials (RCTs). However, practice patterns and GnRFA techniques vary, and no peer-reviewed publication has yet quantified these variations in real-world clinical practice. ObjectiveThis study aims to understand the practice patterns of interventional pain physicians regarding patient selection, use of prognostic blocks, imaging, nerve targets, GnRFA types, and GnRFA techniques in treating knee pain secondary to OA or persistent post-TKA pain. MethodsAn anonymous 29-question survey was distributed via electronic mail to members of the International Pain and Spine Intervention Society (IPSIS) from January 16, 2024, to February 29, 2024. The survey assessed practice patterns related to patient selection, prognostic block use, and GnRFA techniques. Data were collected and stored using REDCap software, with descriptive statistics calculated. ResultsA total of 150 completed surveys were analyzed, representing a completion rate of 2.0 % of surveys sent, 3.5 % of emails opened, and 56.8 % of those who clicked on the survey link. Respondents generally use common selection protocols regarding OA grade (Kelgren-Lawrence 3 and 4), duration of failed conservative care (3–6 months), a single anesthetic block paradigm, and use of fluoroscopic guidance for the GnRFA procedure. More variability was reported between respondents regarding the volume of anesthetic used during prognostic blocks, the threshold to consider a prognostic block “positive,” the technology used, and nerves targeted during the GnRFA procedure. ConclusionThe study provides valuable insights into the current practice patterns of GnRFA among interventional pain physicians. While there is consensus on some aspects of patient selection and procedural techniques, significant variability exists in prognostic block protocols and nerve targets for GnRFA. These findings highlight the need for further research to explore the long-term efficacy and safety of GnRFA and to standardize techniques and protocols across different practice settings, ultimately improving patient outcomes and quality of life. The low response rate may limit generalizability, and the survey did not include data on active tip sizes used for ablation or whether other procedures should be exhausted before resorting to GnRFA. Additionally, a survey to IPSIS membership only may not fully represent a diverse cohort of pain management specialists, potentially introducing sampling bias. Future studies should include members from a broader range of professional organizations to enhance representativeness.

Surface Coating of Nickel-Titanium (Ni-Ti) Pediatric Rotary File Using Graphene Oxide: A Scanning Electron Microscopy Analysis.

The effectiveness of endodontic files relies significantly on the characteristics of the outermost layer, which can be greatly improved through suitable surface treatments and appropriate coatings. Graphene-based materials (GBMs) have been utilized to fabricate nanocomposite coatings aimed at improving surface characteristics and mechanical behavior, including resilience, sustainability, oxidation resistance, solidity, and traction. This research aims to study the surface topography of a nickel-titanium (Ni-Ti)pediatric rotary file coated with graphene oxide (GO) using a scanning electron microscope (SEM). The study utilized Ni-Ti pediatric rotary instruments that were 16 mm long and had the same ISO tip size of #25. The Ni-Ti pediatric rotary files had a titanium oxide coating that needed to be removed for the application of the GO coating. The GO coating was applied to the files using an electrophoretic deposition(EPD) procedure. Data were gathered to evaluate the surface topography and structural profiles of the GO-coated endodontic files through SEM analysis. SEM imaging showed that the GO coatings consisted of numerous layers of GO sheets, which were uniformly and thoroughly applied to the endodontic instrument. A substantial portion of the GO layers aligned with neighboring layers along the edges, creating a continuous structure. GO coatings were effectively applied to Ni-Ti endodontic instruments using EPD. The deposition of the GO coating is consistent throughout the surface of the Ni-Ti rotary instrument.

Impact of Mechanical Stimuli on PEO-Litfsi Stiffness and Ionic Conductivity

Recently a large emphasis has been placed on developing safer electrolytes for lithium-ion batteries as a response to an increase in battery demand. Solid polymer electrolytes, such as those based on polyethylene oxide (PEO) show good resistance to mechanical loading, and when coupled with ceramic fillers demonstrate enhance ionic conductivity as well. Prior to this work, efforts have been made to determine the effects mechanical stimuli have on the stiffness and ionic conductivity of the electrolyte.1–3 However, while previous research has primarily focused on bulk EIS measurements of the electrolyte, here we leverage atomic force microscopy (AFM) to modulate the tip-substrate contact force from a few piconewtons to tens of millinewtons to study the correlation between mechanical loading and ionic conductivity, along with measuring the evolution of the substrate stiffness as a function of mechanical cycling.In this study, we contact the PEO-LiTFSI surface with an electrically conductive Pt-coated tip and mechanically cycle the sample by applying a pre-determined contact force a set number of times. By keeping the contact force and time constant, we extracted the cycle-dependent evolution of the sample stiffness. Results show that stiffness is reduced 30% within the first ten cycles, and then minimally changes with subsequent cycling, matching the results from bulk measurements. Changes in ionic conductivity as a function of mechanical cycling are then measured using electrical characterization techniques. To gain a better understanding of how conductivity and stiffness are evolving, we conducted a parametric study by varying tip size, contact force, and number of mechanical cycles. From early results, we found that electrical resistance increases by ~3% (from 2985 Ohm to 3075 Ohm) after 100 cycles of mechanical force ranging between ~ 0 nN to 450 nN with a 5 µm radius tip. The change in the electrical resistance is believed to originate from the local amorphization of PEO-LiTFSI induced by the mechanical stimuli and resulting change of the local conductivity. These results can be leveraged to further understand how mechanical stimuli affects the mechanical and electrical characteristics of solid electrolytes and help establish a model to predict long-term stability and performance of batteries.This work was supported by the National Science Foundation (#2125640).(1) Yoon, D. et al., ACS Appl. Energy Mater, 6 (18), 9400, 2023(2) Li, X. et al., ACS Appl. Mater. Interfaces, 11 (25), 22745, 2019(3) Liu, L. et al., Nano Energy, 69, 104398, 2020

Characterisation of Intraocular Lens Injectors.

In modern ophthalmic surgery, an intraocular lens (IOL) is commonly implanted into the patient's eye with an IOL injector. Many injectors are available, showing various technological differences, from the early manually loaded injector systems to the modern preloaded injectors. This review aims to give a concise overview of the defining characteristics of injector models and draws attention to complications that may occur during IOL implantation. One can differentiate injectors according to their preoperative preparation (manually loaded or preloaded), their implantation mechanism (push-type or screw-type or combined or automated), the size of the nozzle tip, the presence of an insertion depth control feature, and the injector's reusability. Potential complications are IOL misconfigurations such as a haptic-optic adhesion, adherence of the IOL to the injector plunger, an overriding plunger, uncontrolled IOL rotation, a trapped trailing haptic, or damage to the IOL. Additionally, during IOL implantation, the nozzle can become damaged with scratches, extensions, cracks, or bursts to the tip. While these complications rarely produce long-term consequences, manufacturers should try to prevent them by further improving their devices. Similarly, surgeons should evaluate new injectors carefully to ensure the highest possible surgical safety.

Ion conduction property of track- etched conical nanopores modified by atom layer deposition method under applied pressure

In this work, single conical nanopores in Kapton films were fabricated using the etch-track and atomic layer deposition (ALD) methods. Nanopores with different tip sizes (34 nm, 123 nm, 194 nm, respectively) were used to investigate the effect of pressure on the ionic conduction rectification (ICR) of the nanopores. Results showed that the effect of pressure on the ICR of the nanopores is related to the tip size of the nanopore and the rectification coefficient of the nanopores in the electrolyte solution. When pressure was applied across the nanopore, a volumetric flow Q was engendered through the conical-shaped nanopore. Only when the tip size of the nanopore reached a certain size could the pressure-driven liquid flow eliminate the hydraulic resistance of the pore, changing the ion distribution in the nanopore and further altering the ICR of the nanopore. For nanopores with a tip size of 34 nm, the effect of pressure on ICR was almost negligible. Only when the tip size of the nanopore was greater than a certain extent did the applied pressure significantly affect the ICR. The influence of pressure on ICR was also related to the strength of the rectification coefficient of the nanopore in the electrolyte. Nanopores exhibiting smaller ion rectification coefficients were more susceptible to the effects of pressure on their ICR.

Being all-seeing gymnast within kidney cavity: analysis of the optical and flexibility characteristics trends of 61 flexible ureteroscopes over four decades.

The purpose of this review is to analyze the trend in optical features and flexibility changes of flexible ureteroscopes over the past decades, and determine the correlation of individual parameters with release period as well as with dimensional parameters. Flexible ureteroscopes mentioned in the literature or those commercially available were searched. To minimize the search bias, the instruments were grouped by release date time-periods of < 2000 year, 2000-2009, 2010-2019, and 2020 onwards. The final review included only those instrument models for which data on minimum and maximum depth of field, field of view, direction of view, and deflection degree had been determined. The correlation among features investigated as well as with release period was also determined. 61 models of flexible ureteroscopes (27 fibreoptic and 34 digital scopes) were included. Among the different features investigated among fiberoptic endoscopes, minimum depth of field positively and negatively correlated with channel size and field of view, respectively, whereas maximum depth of view and field of view positively correlated with overall shaft and deflection degree, respectively. Up and down deflection strongly correlated with each other and both were negatively proportional to the distal tip size. For the digital endoscopes, minimum depth of field negatively and positively correlated with distal tip size and working length, respectively. Maximum depth of field positively correlated with field of view, whereas the latter was negatively proportional to the overall shaft. As for the fiberoptic counterparts, up and down deflection strongly correlated with each other. Field of view, up and down deflection of fiberoptic flexible ureteroscopes, were significantly increased among fiberoptic and digital endoscopes over decades. As flexible ureteroscopy technology has evolved, there has been a trend towards increasing field of view with up and down deflection. Given the importance of scope ergonomics, one aspect of this popularity is the improvement of optical characteristics and deflection degree, which significantly correlates with the release period.

Effect of Cross-Sectional Designs of Different Ni-Ti Files on Shaping Ability After Repeated Usage in Simulated Root Canals.

Background and Objective: The study aimed was to compare the effect of cross-sectional designs of five rotary systems (One Curve, 2Shape, K3-i File, E3 Azure, Neolix), on the shaping ability of the files in simulated resin blocks under controlled conditions with five repeated use. The shaping ability of the files includes the following variables: (1) Longitudinal sectional area difference, (2) Canal wall surface area difference, (3) Canal volume difference, (4) SMI (structure material index) difference, (5) Cross-sectional area difference. Methods: Five rotary file systems: (1) One Curve, (2) 2Shape, (3) K3-i File, (4) E3 Azure, (5) Neolix, were tested in simulated J-shaped root canal resin blocks with a 45˚ angle of curvature. 10 files from each system, each one of the 10 files were used to prepare 5 resin blocks, named R1-R2-R3-R4-R5. All the used files from the 5 systems had tip size 25 diameter, and taper (6%), and length (25 mm). The first 4 rotary systems were used with a fixed speed (350 rpm), and fixed torque (3 Ncm), except for the fifth system which was used with a speed of (500 rpm), and torque (4 Ncm), Following the manufactural recommendation of each system. All the 250 resin blocks were prepared for Glide Path with manual reamers size 10, and 15, with a fixed working length 16 mm, then all the 250 samples were prepared with a Proglider rotary file from Dentsply (size 16 taper 3%), then finally were prepared with Edge Files (USA), with size 20 and taper 6%, reaching to the step of master preparation with the selected files of the 5 systems. Using a customized device for preparation to ensure fixed vertical force and to exclude any lateral force, preparation was done with EDTA solution as irrigation, with a fixed no. of 4 strokes for the first 5 systems and 9 strokes for the Neolix, the time was controlled by using a Metronome, each stroke duration was 6 seconds. Results: In the first, second, third, and fourth variables a statistically non-significant difference (P &gt; 0.05) was found between One curve and 2Shape, a statistically significant difference (P &lt; 0.05) was found between One Curve, K3-i File, E3 Azure, and Neolix. About the fifth variable which is the Cross-sectional area difference: the study compared the difference between the cross-section area of the canal at the point D8, comparing the cross-section area before and after preparation using ANOVA test and Post hoc test, a statistically significant difference (P &lt; 0.05) was found between the Neolix and (2shape, K3 i-File, and E3 Azure). Conclusion: The cross-sectional design of the endodontic rotary instrument had an obvious effect on the shaping ability of the system. Keywords: Cross-sectional design, Shaping ability, Nickle Titanium rotary files (One Curve, 2Shape, K3-i File, E3 Azure, Neolix).

Enhanced fracture toughness of Ti2AlNb/Ti6Al4V layered metal composite

Drawing inspiration from the intricacies of nacre structure, Ti2AlNb/Ti6Al4V layered metal composite was fabricated by vacuum hot pressing and achieved high fracture toughness. The fracture toughness of the composite registers at 48.5 MPa∙m1/2, surpassing the theoretical fracture toughness calculated based on the rule of mixture (ROM) and exhibiting 54 % improvement compared toTi2AlNb alloy. The introduction of a layered configuration imparts complex crack propagation pathways to the composite. The occurrences of crack deflection, crack bridging, crack passivation, and interface delamination serve to increase the resistance to crack propagation. Moreover, the plastic deformation of the ductile Ti6Al4V layer and the large plastic zone size of the crack tip can release the stress concentration and delay the fracture of the composite. This understanding not only advances our comprehension of the toughening mechanisms but also has practical implications for the application and development of layered Ti2AlNb alloys.

The ophthalmologic crescent blade in endonasal surgery.

The angled tip and small size of the crescent blade provide versatility for its use in a variety of endonasal procedures. The crescent blade enables cutting along 180° from the tip, ensuring a tangential cut through the mucosa, which is important for flap viability. The disposable nature of the blade ensures that it is always sharp, allowing for its use in mucosal and cartilaginous cuts.

Dynamic Photoelastic Analysis of Stress Distribution in Simulated Canals Using Rotary Instruments with Varied Tip and Taper Sizes: A Quasi-3D Approach

IntroductionTo compare the stress produced on the walls of simulated canals by rotary instruments with varied tip and taper sizes. MethodsNinety isotropic transparent blocks, each containing a 60-degree curved canal, were distributed into 18 groups (n = 5) based on the instrument tip (sizes 10, 15, 20, 25, 30, and 35) and taper (sizes 0.02, 0.04, and 0.06). The blocks were fixed in a circular polariscope setup for dark field analysis. A digital camera was employed to capture the real-time birefringence patterns generated by each instrument. Digital image frames, corresponding to the instrument reaching the end of each canal third, were extracted and evaluated by 2 independent observers for the stress generation on canal walls. The data analysis employed a semi-quantitative scale ranging from 0 to 5. Cohen's Kappa coefficient test was used to determine the inter-observer agreement while the results were compared using Kruskal–Wallis test followed by an all-pairwise posthoc procedure (α = 5%). ResultsInter-observer agreement was 0.95. A significant influence of the tip size on stress was observed across the coronal (P = .011), middle (P = .006), and apical (P = .026) thirds. In contrast, taper size did not affect the stress induced at the coronal (P = .509), middle (P = .958), or apical (P = .493) thirds. The variations in tip and taper sizes did not result in a significant stress differences among the thirds (P = .181). ConclusionsThe stress significantly increased across all canal thirds with larger tip sizes of rotary instruments, whereas the taper sizes did not influence the stress when compared to the canal thirds.

Simulation of liquid cone formation on the tip apex of indium field emission electric propulsion thrusters

Field emission electric propulsion (FEEP) thrusters possess excellent characteristics, such as high specific impulse, low power requirements, compact size and precise pointing capabilities, making them ideal propulsion devices for micro-nano satellites. However, the detection of certain aspects, such as the evolution process of the liquid cone and the physical quantities at the cone apex, proves challenging due to the minute size of the needle tip and the vacuum environment in which they operate. Consequently, this paper introduces a computational fluid dynamics (CFD) model to gain insight into the formation process of the liquid cone on the tip apex of indium FEEP. The CFD model is based on electrohydrodynamic (EHD) equations and the volume of fluid (VOF) method. The entire cone formation process can be divided into three stages, and the time-dependent characteristics of the physical quantities at the cone apex are investigated. The influences of film thickness, apex radius size and applied voltage are compared. The results indicate a gradual increase in the values of electrostatic stress and surface tension stress at the cone apex over an initial period, followed by a rapid escalation within a short duration. Apex configurations featuring a small radius, thick film and high voltage exhibit a propensity for liquid cone formation, and the cone growth time decreases as the film thickness increases. Moreover, some unstable behavior is observed during the cone formation process.

Crack tip shielding and size effect related to parallel edge cracks under uniaxial tensile loading

The present work aims at investigating crack shielding and size effect related to a cracked slab under tensile loading. For this purpose, experimental tests are carried out on PMMA cracked samples. Three different geometries are taken into account, presenting one, two or three parallel edge cracks, and assuming their distance equal to their initial length. Results are interpreted through the coupled stress and energy criterion of Finite Fracture Mechanics (FFM). The approach is implemented numerically, and parametric finite element analyses are carried out to evaluate the normal stress field and the stress intensity factor for each configuration. It is found that asymmetric crack propagation has to be preferred according to the energy balance. The matching between FFM failure predictions and experimental data reveals to be satisfactory.

Size control of InP nanowires by in situ annealing and its application to the formation of InAsP quantum dots

We carried out in situ annealing of InP nanowires (NWs) in a metal-organic vapor phase epitaxial (MOVPE) growth reactor to control and reduce the tip size of InP NWs. InP NWs were grown by selective-area (SA) MOVPE on partially masked (111)A InP substrates, and annealing was successively applied in tertiarybutylphosphine (TBP) ambient. Initially, the InP NWs had a hexagonal cross-section with {112¯} facets vertical to the substrates; they became tapered, and the edges were rounded by annealing. By appropriately selecting the annealing temperature and initial NW diameter, the tip size of the NW was reduced and NWs with a tip size of 20 nm were successfully formed. Subsequently, a thin InAsP layer was grown on the annealed NWs and their photoluminescence was investigated at low temperatures. The characterization results indicated the formation of InAsP quantum dots (QDs) emitting in the telecom band. Our approach is useful for reducing the size of the NWs and for the controlled formation of InAsP QDs embedded in InP NWs in photonic devices compatible with telecom bands.

A Classical Molecular Dynamics Study of the Effect of the Atomic Force Microscope Tip Shape, Size and Deformation on the Tribological Properties of the Graphene/Au(111) Interface

Atomic force microscopes are used, besides their principal function as surface imaging tools, in the surface manipulation and measurement of interfacial properties. In particular, they can be modified to measure lateral friction forces that occur during the sliding of the tip against the underlying substrate. However, the shape, size, and deformation of the tips profoundly affect the measurements in a manner that is difficult to predict. In this work, we investigate the contribution of these effect to the magnitude of the lateral forces during sliding. The surface substrate is chosen to be a few-layer AB-stacked graphene surface, whereas the tip is initially constructed from face-centered cubic gold. In order to separate the effect of deformation from the shape, the rigid tips of three different shapes were considered first, namely, a cone, a pyramid and a hemisphere. The shape was seen to dictate all aspects of the interface during sliding, from temperature dependence to stick–slip behavior. Deformation was investigated next by comparing a rigid hemispherical tip to one of an identical shape and size but with all but the top three layers of atoms being free to move. The deformation, as also verified by an indentation analysis, occurs by means of the lower layers collapsing on the upper ones, thereby increasing the contact area. This collapse mitigates the friction force and decreases it with respect to the rigid tip for the same vertical distance. Finally, the size effect is studied by means of calculating the friction forces for a much larger hemispherical tip whose atoms are free to move. In this case, the deformation is found to be much smaller, but the stick–slip behavior is much more clearly seen.